1. Field of the Invention
This invention relates generally to efficient in vivo and in vitro production of immunoglobulin-producing avian cell lines. More particularly, this invention concerns a method of transforming chicken B-lymphocytes using a reticuloendotheliosis virus or a v-rel gene with subsequent proliferation of B-lymphocytes that produce immunoglobulins with high efficiency.
2. Description of Related Art
Reticuloendotheliosis viruses (REVs) are a group of avian retroviruses that infect chickens, turkeys and ducks (1). The prototype virus of this group is reticuloendotheliosis virus strain T (REV-T). REV-T is highly oncogenic and causes peripheral nerve lesions and visceral reticuloendotheliosis in susceptible birds (2). The tumors caused by the infection develop rapidly, appear to be polyclonal and apparently require the expression of the v-rel oncogene carried by REV-T (3, 4).
Although the REV-T virus transforms appropriate target cells, it is replication defective and requires a helper virus for its propagation. REV-A is one example of a so-called non-(replication) defective helper virus. Such helpers are distinguished from REV-T by their ability to replicate in vitro in fibroblasts and their inability to induce acute neoplastic disease n vivo (5, 6). However, some of the helper viruses, chick syncytial virus (CSV) and REV-A, for example, independently induce a bursal-dependent B-cell lymphoma that is indistinguishable from avian leukosis virus (ALV)-induced lymphoid leukosis (6, 7). ALV and CSV are genetically unrelated but function similarly in exhibiting similar interactions with the same host oncogene in B lymphomas. These lymphomas are characterized by long latency periods, are monoclonal, and have a proviral integration of a promoter-enhancer sequence near the proto-oncogene c-myc in a susceptible cell (8, 9).
Despite numerous studies on avian cells transformed by REV-T, the identification of the target cells for the virus has not been clarified. In vitro transformed cell lines developed after infection of isolated spleen cells with REV-T(REV-A) appeared to have characteristics of immature B-lymphocytes (2, 10, 11) but the absence of specific markers that define this phenotype have prevented conclusive identification. The principal target cells transformed by REV-T(REV-A) both in vivo and in vitro have generally been believed not only to be extremely immature lymphoid cells of B-line lineage but also to fail to synthesize immunoglobulin molecules (12). Rare exceptions have been reported, but efficiency of IgM production was very low and no transformed cell was observed to synthesize detectable levels of IgG or IgA (11).
Nevertheless, a method of efficient production of antibody-producing cell clones would be useful for a variety of purposes. These include models for the study of cellular and genetic mechanisms involved in leukemogenesis, hematopoietic cell differentiation and monoclonal antibody production. Additionally, the development of monoclonals isolated from chicken antibody cell lines would offer several particular advantages. First, the chicken is more phylogenetically distinct from man than the commonly used mouse, so that chicken monoclonals could be developed against important human antigens more easily than mouse monoclonals against such antigens. Second, the allotypic heterosera traditionally used to recognize mouse antigens are weak and difficult to produce, but could be conveniently and easily recognized by chicken monoclonals; third, the epitopes generated by the chicken during infection with defined pathogens could be useful in developing effective vaccine strategies; and fourth, in many cases tumor specific antigens found on avian tumors should be recognized by the chicken, leading to understanding of tumor regression in several avian systems.
Therefore, identification of the target cells for v-rel-induced tumors and development of methods of efficient antibody production from avian cell clones would be useful not only for the reasons cited but also in developing analogous strategies in the in vivo and n vitro production of monoclonal antibody producing clones from other types of cell lines.